The present invention is related to the following commonly assigned pending U.S. patent applications: COMPACT FLUID COUPLER FOR THERMAL INK JET PRINT CARTRIDGE INK RESERVOIR, Ser. No. 07/853,372, filed Mar. 18, 1992, by James G. Salter et al.; INK PRESSURE REGULATOR FOR A THERMAL INK-JET PRINTER, Ser. No. 07/928,811, filed Aug. 12, 1992, by Tofigh Khodapanah et al.; COLLAPSIBLE INK RESERVOIR STRUCTURE AND PRINTER INK CARTRIDGE, Ser. No. 07/929,615, filed Aug. 12, 1992, by George T. Kaplinsky et al.; TWO MATERIAL FRAME HAVING DISSIMILAR PROPERTIES FOR A THERMAL INK-JET CARTRIDGE, by David S. Swanson et al., Ser. No. 07/994,807, filed Dec. 22, 1992; COMBINED FILTER/AIR CHECK VALVE FOR THERMAL INK-JET PEN, by George T. Kaplinsky, Ser. No. 07/995,109, filed Dec. 22, 1992; DOUBLE COMPARTMENT INK-JET CARTRIDGE WITH OPTIMUM SNOUT, by David W. Swanson et al., Ser. No. 07/995,221, filed Dec. 22, 1992; THERMAL INK-JET PEN WITH A PLASTIC/METAL ATTACHMENT FOR THE COVER, by Dale D. Timm, Jr. et al., Ser. No. 07/994,810, filed Dec. 22, 1992; NEGATIVE PRESSURE INK DELIVERY SYSTEM, George T. Kaplinsky et al., Ser. No. 07/995,851, filed Dec. 23, 1992; THIN PEN STRUCTURE FOR THERMAL INK-JET PRINTER, by David W. Swanson et al., Ser. No. 07/994,808, filed Dec. 22, 1992; SPRING-BAG PRINTER INK CARTRIDGE WITH VOLUME INDICATOR, David S. Hunt et al., application Ser. No. 07/717,735, filed Jun. 19, 1991; U.S. Pat. No. 5,359,353, and SIDE BIASED PEN DATUM SCHEME FOR THERMAL INK-JET CARTRIDGE, by David S. Swanson et al., Ser. No. 08/057,241, filed Apr. 30, 1993; the entire disclosures of which are incorporated herein by this reference.
The present invention relates to thermal ink-jet (TIJ") pens characterized by a high volumetric efficiency in a thin pen package.
In any office product the overall size of the product has an effect on the cost and sell appeal of the product. In the thermal ink-jet printer market, the foot print of a personal printer is a key selling point if the printer can be made small enough to fit on a customer's desk top. In previous printers marketed by the assignee of the present invention, Hewlett-Packard Company ("HP"), such as the Paintjet XL and the Paintjet XL300, the printers are relatively large and typically are placed on a side table off the customer's desk due to their size. The HP Deskjet has a small footprint and is commonly placed on the customer's desk. The HP Deskjet is a single pen device and therefore the footprint is kept small. It is a goal of the present invention to permit a four pen color printer to have a footprint similar to such prior single pen printers.
When a thermal ink-jet product prints onto a page, the pen carriage must travel across the page such that every nozzle of every pen has an opportunity to reach the full paper area. In ink-jet devices, the paper is generally driven along one axis of motion and the pen is driven along a pen scan axis extending 90 degrees to the paper drive axis. This invention addresses shortening the travel along the pen scan axis.
For a single pen product, such as the HP Deskjet, the pen axis must travel the width of the paper plus the width of the pen head. For a four pen product, the pen axis must travel the width of the paper, plus the width of the four pens plus the space between the pens required to mount them. In this case the minimum product width is the paper width plus about twice the width of the pen carriage. The paper width is fixed (unless it is driven relative to the pens by a third axis of motion). In previous foam based pens, the pen width was about 1.25 inches and the pen mounts require about 0.2 inches per pen. In a four pen product this added up to a carriage width of 6 inches. This invention allows pens with the same amount of ink delivered to be narrow, e.g., 0.5 inches, and deliver the same ink volume with a carriage width of about 2.8 inches. This amounts to a reduction in the required product width of at least 6.4 inches, in this example.
As the product width is reduced, the volume of material required for fabrication and the size of plastic parts go down, reducing the molding machine size and thus the molding cost. The pen carriage is supported by beams that must span the length of travel. As the length of travel increase, the stiffness requirements of those beams cause their cross-sections, and thus their cost, to also increase. Thus any decrease in the spanned length is a cost benefit.